CELL

Transport mechanisms

  • Means by which substances from the blood enter the cell
  • Passive, Active, Vesicular

Diffusion

  • Passive process
  • Random mixing
  • Random movement in net movement
  • Kinetic energy

Simple diffusion

  • Passive process
  • Move freely WITHOUTthe help of membrane transport proteins
  • Hydrophobic & non-polar molecules
  • O2, co2, Nitrogen gasses, fatty acids, steroid, fat-soluble vitamins (A,D,E,K)

facilitated diffusion

  • Assists a specific substance
  • Carrier proteins COMBINE with substances
  • Always moved higher to lower
  • Could either be channel or carrier
  • Exhibits : specificity . saturation, competition

Channel-mediated facilitated diffusion

  • Solute move down its concentration gradient
  • Most are ion channels
  • Selective for K or Cl ions

Ion channels

  • Allow passage of small inorganic ions

Gated channel

  • Part of the channel protein acts as a plug

Secondary Active Transport

  • Establishes an ion concentration gradient
  • Symport & Antiport
  • Sugars, amino acids,

Exocytosis

  • Release content outside of the cell (extracellular matrix)
  • Requires ATP
  • Proteins and water-soluble
  • Ex: digestive enzymes, hormones, neurotransmitters, granular secretions : are transported out

Bulk-phase endocytosis / Pinocytosis

  • Occurs in the intestines and kidneys
  • Contain droplet of extracellular fluid
  • “Pinches off”

Active transport

  • Transport against concentration gradient
  • Need ATP
  • Need specific carrier proteins
  • Primary and secondary
  • Na, K, Ca

Two sources of cellular energy

  1. Hydrolysis of ATP
  2. Energy stored in ionic concentration gradient

Primary Active transport

  • Derived from hydrolysis of ATP
  • “Pumps” a substance against concentration gradient

Pump

  • Carrier proteins
  • Mediate primary active transport

Sodium-Potassium pump

  • Most prevalent primary active transport
  • Expels sodium and brings in potassium

secondary active transport

  • Uses energy stored in an ionic concentration gradient
  • ATP is indirectly used
  • Symporters
  • Antiporters

Symporters - same direction

Antiporters - opposite direction

Passive transport

  • Follows law of osmosis
  • No need atp
  • No need carrier
  • 1. Diffusion
  • 2. Osmosis
  • 3. Facilitated diffusion

Phagocytes

  • Carry out phagocytosis
  • Types :
  • 1. Macrophages
  • 2. Neutrophils

Macrophages

  • Located in body tissues

Neutrophils

  • Participles binds to a plasma membrane receptor

Pseudopods
- surround the particle outside the cell

Phagosome

  • Membranes fuse to form a vesicle
  • Fuse with lysosomes
  • Vesicles formed from phagocytosis

Residual body

  • Undigested material

Lipofuscin granules

  • Where residual bodies are remained stored

Exocytosis

  • Release in the extracellular fluid
  • Two types of cells:
  • 1. Secretory cells
  • 2. Nerve cells

Secretory cells

  • Liberate digestive enzymes, hormones, mucus, others.

Neurotransmitters

  • Releases neurotransmitters

Transcytosis

  • Undergo endocytosis and exocytosis on the other end
  • Occurs in the endothelial cells

Isosmotic

  • Equal osmotic pressure

Osmosis

  • Net movement of solvent through selectively permeable membrane
  • Higher to lower
  • Water diffuses across a selectively permeable membrane
  • Water moves from intestines into the blood
  • Water diffuses through lipid bilayer
  • Two ways:
  • 1. Moving between neighboring phospholipid
  • 2. Through Aquaporins

Osmotic pressure

  • Must be applied to stop fluid movement

Tonicity

  • Change the volume by altering water content
  • Isotonic, hypotonic, hypertonic

Isotonic

  • Cannot cross plasma membrane
  • .85 to .90%
  • Water enter and exit at the same rate
  • Normal RBC

Hypotonic

  • Low solute
  • Water enter faster
  • Swelling to bursting
  • Lysis
  • Pure water is very hypotonic

Hypertonic

  • High solute
  • Water exit faster
  • Causes Crenation : means shrinkage of cells

Peroxisome

  • Breaks down hydrogen peroxide
  • Site of lipid and amino acid degradation

Nucleus

  • Control center
  • Regulates protein synthesis
  • Enclosed by nuclear envelope
  • Contains chromatin

Chromatin

  • Thin strands of DNA

Nucleolus

  • Ribosome synthesis
  • Regulates rate of cell division

Plasma membrane

  • Lipid bilayer composed of : phospholipids and cholesterol
  • Outer boundary
  • Controls entry and exit
  • Receptor proteins
  • Intracellular communication
  • Marks molecules

Ribosome

  • Protein synthesis

Free ribosomes

  • Distributed throughout the cytoplasm

Rough endoplasmic reticulum

  • Synthesizes proteins and transport to golgi apparatus

Smooth endoplasmic reticulum

  • Detoxifies harmful chemicals
  • Manufactures lipids and CHO

Golgi apparatus

  • Flattened membrane sacs stacked on each other
  • Modifies, packages, distributes protein and lipids for secretion

Lysosome

  • Contains digestive enzymes

Proteasomes

  • Tube-like protein complexes
  • Break down proteins

Centrioles

  • Centers for microtubule formation
  • Determine cell polarity
  • Basal bodies of cilia and flagella
  • Pair of cylindrical organelles
  • Located in Centrosome

Centrosome

  • A specialized area where microtubule formation occurs

Flagellum

  • 55 micrometers
  • Propels spermatozoa

Cilia

  • 10 micrometers
  • Move materials over the surface

Microvilli

  • Increase surface area for absorption and secretion
  • To form sensory receptors

Mitochondria

  • Spherical, rod shaped, threadlike
  • Inner membrane forms projections called CRISTAE
  • ATP synthesis when OXYGEN is available

Vesicular transport

  • 1. Endocytosis
  • 2. Exocytosis

Endocytosis

  • Forms a vesicle
  • Requires ATP
  • Phagocytosis - takes in solid
  • Pinocytosis - takes in liquid

Factors affecting diffusion

  • Steepness of the concentration gradient
  • Temperature
  • Surface area
  • Diffusion distance

Receptor-mediated endocytosis

  • Highly selective type of endocytosis
  • Process:
  • Binding
  • Vesicle formation
  • Uncoating
  • Fusion with endosome
  • Recycling of receptors
  • Degradation in lysosomes

Phagocytosis

  • Engulfs large solid particles ( worn-out cells, bacteria, viruses

Pseudopods

  • Surround the particle outside the cell

Principle of osmosis

  • Water move through selectively permeable membrane
  • Move from left arm to right arm down the water concentration gradient
  • Includes:
  • Isosmotic , Osmotic pressure, Tonicity